Cancer is mostly caused by factors like environmental influences, according to a study published Wednesday. Such "extrinsic" factors amount to 70 percent to 90 percent of all cancers, said researchers at Stony Brook University in New York.

The study disputes research published in January that attributed most cancers to "bad luck," or in more scientific terms, random mutations that by chance lead to cancer.

That study sparked controversy because of its implication that little could be done to prevent most cancers. Performed by Bert Vogelstein and Cristian Tomasetti of Johns Hopkins University, it found a striking correlation between the incidence of various cancers and the number of stem cell divisions in the tissues the cancers arose from.

The more divisions, and hence the chance of mutations in the process, the higher the cancer rate. That explains why the incidence of skin cancers is so much greater than that of bone cancers, the original study found.

The new study, published in the journal Nature, analyzed those findings. It concluded that the rate of intrinsic mutation was too low to account for the observed rate of cancer. So environmental factors, such as exposure to carcinogens, must account for the great majority of cancers.

Yusuf A. Hannun was the study's senior author. Song Wu was the study's first author.

This new information provides more insight into cancer, but won't settle the dispute, said scientists interviewed by Genetic Expert News Service. And the original study's authors say it doesn't contradict their findings, or suggest any plausible alternative explanation.

"These are interesting calculations and give us a sense of the possible range of effects," said Giles Hooker, Associate Professor, Department of Biological Statistics and Computational Biology, at Cornell University. "However, they rely on a very simplified model of cancer mutation and the resulting numbers should at best be regarded as ballpark estimates."

Hooker said the new study took the lowest baseline estimate of mutations to calculate intrinsic cancer risk, and assumed that any cancers in excess of that rate were caused by environmental factors.

"However, we don’t know how tissues differ in their intrinsic mutation rates," Hooker said. "Thus in the authors’ model, a tissue that is more prone to mutations may still be categorized as having high environmental risk."

Another scientist gave a more positive opinion.

"This Nature report presents a strong counterargument to a report published earlier this year in Science which began a debate about whether the majority of people who develop cancers do so because of 'bad luck,' " said Jian-Min Yuan, Associate Director for Cancer Control and Population Sciences at the University of Pittsburgh Cancer Institute.

"The current epidemiological evidence strongly supports an important role of environmental factors in the development of cancer," Yuan said. "For example, people who stop smoking at 55 years would cut their lung cancer risk by half compared with those who continue smoking by 85 years of age. HBV vaccine has resulted in the reduction of hepatocellular carcinoma incidence by 70%.

"These results demonstrate that a large proportion of cancer is caused by environmental factors and are preventable if their underlying environmental causes are identified."

In their reply, original study authors Vogelstein and Tomasetti said the new study didn't offer any environmental explanation for the relationship between the number of stem cell divisions in a tissue and its cancer rate.

Moreover, they said in a blog post that the Hannun study came to conclusions at variance with well-established facts about the origins of certain cancers.

Hannun's study concluded that more than 99 percent of prostate cancers, more than 98 percent of thyroid cancers and the more than 90 percent of other cancers are caused by environmental factors, the post said. However, epidemiologists have already determined that less than 1 percent of these cancers can be attributed to extrinsic factors, Vogelstein and Tomasetti wrote.